This invention relates to a robotic admixture system for admixing medications into a dispensing container for dispensing to a patient.
Many medications are dispensed to a patient from an IV bag into which a quantity of the medication is introduced generally in admixture with a diluent. In some cases the IV bag contains only the medication and diluent. In other cases the IV bag also contains a carrier or other material to be infused into the patient simultaneously with the medication. Medication can also be dispensed from a syringe.
Medication is generally supplied in powder form in a medication container or vial. A diluent liquid is also supplied for admixture with the medication in a separate or diluent container or vial. As is well known to the pharmacist, different medications require different diluents and different prescriptions require different amounts of diluent and different amounts of the admixture for submission to the patient.
One repetitious function of the pharmacist is therefore to prepare dispensing containers, generally IV bags, containing the prescription for the different patients to be supplied from the pharmacy. Many IV bags of this type require a single medication which is repeated in a number of the IV bags for example insulin which is of course dispensed to many different patients. In such cases it is not necessary to tailor the prescription to the individual patient so that a number of similar IV bags containing the same medication can be prepared in a batch.
Other drugs and particularly chemotherapy drugs require very accurate and careful control of the prescription so that it is necessary to carefully tailor the prescription to the individual patient.
In order to prepare a dispensing container of the medication, the pharmacist takes a vial of the medication as prescribed and one or more vials of the diluent to be admixed therewith. The pharmacist then draws from the diluent container a predetermined quantity of the diluent into a sterile disposable syringe by passing the needle into the vial through the elastic membrane closing the vial. In order to extract the liquid from the vial it is necessary to replace the extracted liquid with air and therefore the syringe is actuated repeatedly to pump air into the vial and to extract liquid from the vial until the required quantity is extracted as measured by the markings on the syringe. A syringe is chosen of a suitable size so that the amount to be extracted constitutes a significant proportion of the total volume of the syringe in order to provide an accurate measurement. The pharmacist therefore must before starting select the medication vial of the required size, the diluent vial or vials of the required size and also a syringe of the required size.
After the filling the syringe to the required amount of diluent, the pharmacist then injects the diluent into the medication container again penetrating the elastic membrane with the needle and again repeatedly injecting liquid and withdrawing air until the total quantity of the required diluent is introduced into the medication container.
The pharmacist then effects a shaking action on the medication container until the medication and diluents are properly mixed. In some cases this is relatively straight forward. In other cases extensive shaking of the container is required. In yet further cases extensive shaking is required together with extended periods of standing to obtain the complete admixture necessary. Mechanical shaker devices are available of various different designs to assist in the shaking action which can otherwise become physically demanding.
When the medication is fully mixed with the diluent, it is again necessary to withdraw from the medication container a required quantity of the admixed medication and a diluent for insertion into the dispensing container. This is again effected by the disposable sterile syringe which is utilized to repeatedly inject air and remove liquid until the required quantity of the liquid is withdrawn into the syringe. This required quantity is then dispensed into the dispensing container and generally the use of an IV bag allows the liquid to simply be injected into the IV bag without concern for pressures since the IV bag is flexible. In some cases the syringe itself is used as the dispensing container so that there is no need for the final step of supplying the medication into the dispensing container.
It will be appreciated, therefore, that this process is relatively lengthy and physically demanding, leaving significant potential for error in view of this combination.
It has been previously been proposed that a robotic ad-mixture system be developed which enables the dispensing containers to be filled with the required quantity of the required admixture of diluent and medication. One published proposal is set forth in the American Journal of Hospital Pharmacy Vol 46 November 1989 which discloses preliminary work carried out by some of the inventors in the present application.
This preliminary work disclosed the use of a robot arm and a syringe manipulation head which receives a syringe of a predetermined size and activates the plunger of the syringe to withdraw and expel liquids into the required containers. The head is rotatable about a horizontal axis so that the syringe can be inverted for withdrawing liquids and can face downwardly for dispensing the liquid.
However this work was only of a preliminary nature and did not provide a fully functioning system including all of the required steps to lead to a commercially viable robotics system.
The only other work in this area which is known to have occurred is that carried out in Red Deer, Alberta, Canada and shown in Canadian patent 1,317,262 issued on May 4th, 1993 to the inventors Zesulka et al which proposes a system for a pharmacy which handles the medication and diluent containers and manipulates these to the required positions for admixture. It is believed that the system includes a complex double ended needle arrangement which allows injection of the diluent into the medication container. However this system has not led to a commercial construction and is currently believed only to be in the proposal stage.